This invention refers to a method for reversing the rotation and to an electronic apparatus for controlling the ignition of an internal combustion engine of two-stroke type, and in particular relates to a microprocessor-controlled electronic apparatus for reversing the rotation of engines, both of single-cylinder and two-cylinder type, obtaining the necessary information on the phase and the rotational direction of the engine by using a particular magnetic sensor and the same voltage generator which powers the ignition circuit of the engine. The invention can be used for reversing the rotation in engines for snowcats, small vehicles, aquascooters and in all those applications which call for a controlled reversal of the rotation of a two-stroke engine.
Mechanical systems or electric and electronic devices of varying complexity have been variously proposed to control the reversal of a two-stroke internal combustion engine.
In particular, U.S. Pat. Nos. 5,036,802, 5,782,210 and 5,794,574, show a number of devices for reversal of the rotation of an engine, comprising a microprocessor appropriately programmed for monitoring the speed and direction of rotation of the engine, as well as for managing the ignition of the engine, both during its forward rotation and during its reverse rotation, on the basis of information obtained by sampling the output of a voltage generator, or on the basis of pulse signals, separate from the voltage signals of the generator, supplied by a pair of inductive triggers suitably out of phase to provide the control microprocessor with information relating to the direction, speed of rotation and phase of the engine.
In general, the previously known reversing devices require complex, costly electronic solutions which are somewhat unreliable or in any case difficult to set when the reversal must be carried out at very low speeds of rotation; in particular, in the previously known rotation reversing devices, the ignition must be deactivated beforehand to cause the engine to slow down and the pulse signals are generated by usual magnetic detectors of inductive type, which have the capacity to sense the variation in the magnetic flux generated by them, caused by the passage of a tooth provided on the peripheral surface of the rotor of the voltage generator which normally powers the ignition of the engine.
It is also known that in the sensors operating by this principle, each variation in the magnetic flux gives rise to the generation of an electric pulse having a polarity corresponding to a positive or a negative variation of the magnetic flux; that is to say, a positive and, respectively, a negative signal depending on whether the tooth is entering or leaving the magnetic field of the sensor, regardless of the direction of rotation. Hence, by using a single sensor of this type it is not possible to know the rotational direction of the engine under all the conditions which in practice may exist at the time of reversal; in fact if the reversal time coincides with an intermediate position of the tooth, with respect to the axis of the sensor, that is to say when the tooth has already magnetically engaged the sensor, the latter will in any case emit two signals of opposing polarities, likewise to the case in which the tooth continues its forward rotation, thereby making it impossible to recognize the direction of rotation and to efficiently control the ignition of the engine.
In the electronic control of the reversal of rotation of an engine it is also necessary to be fully acquainted with the angular position of the engine in relation to the thermal cycle, in that it is essential data not only for controlling the ignition in both rotational directions of the engine, but also for controlling the entire reversal process and the subsequent reattempts in the event of a failed one.
In the devices described in the previous patents, the amplitude of the pulse generated by the inductive type sensors is proportional, as is known, to the derivative of the magnetic flux, that is to say, depending upon the speed at which the tooth enters and, respectively, leaves the magnetic field of the sensor; hence, for low speeds of rotation the amplitude of the pulse generated may sometimes prove to be too low to enable it to be recognized by the control unit, precisely as a result of an attempt at reversal which, as is obvious, involves a time instant in which the speed is zero.
Considering that the aforementioned devices refer precisely to these pulses to obtain information on the phase and direction of rotation of the engine, this can be considered as their critical state.
Consequently, the inductive type sensors normally used in control devices for reversal of the rotation of an internal combustion engine described in the aforementioned patents, are extremely difficult to set in order to obtain a reliable reversal procedure, and are structurally complex and expensive due to the need to use several sensors of a relatively high cost.
The main object of this invention is to provide a method and an electronic apparatus for reversal of the rotation of a two-stroke internal combustion engine, and for controlling the ignition, whereby it is possible to have a high degree of certainty in recognizing both the angular position and the direction of rotation of the engine, regardless of the forward or rearward direction of rotation and the speed of rotation of the same engine, and which ensures a high degree of reliability of the reversing procedure.
A still further object of the invention is to provide a method and an electronic apparatus of the abovementioned type, whereby it is possible to recognize whether an attempt to reverse the rotation of the engine has been successful or has failed, and in this latter case enabling a subsequent attempt or more attempts to be made.
A still further object of the invention is to provide an apparatus for reversal of the rotation of an engine and for controlling the respective ignition system which, in addition to being more highly reliable, is also structurally simple and relatively reduced in cost.
According to a first aspect of the invention, a method has been provided for reversing the rotation of a two-stoke internal combustion engine having a voltage generator to generate an alternate voltage having different polarities for an ignition circuit, and an electronic control apparatus comprising a micro-processor control unit for controlling the alternate voltage supplied to said ignition circuit, in which the reversal of rotation is performed after a reduction of the rotational speed of the engine, comprising the steps of:
providing said control apparatus with a bistable sensor having first and second conductive states, and cyclically switching the sensor between said first and second states during the rotation of the engine;
generating a first binary signal having first and second operative levels correlated to said first and second conductive states of the bistable sensor;
generating a second binary signal having first and second operative levels correlated to the polarities of the alternate voltage supplied to the ignition circuit;
detecting speed and direction of rotation of the engine, on the basis of information obtained by the microprocessor control unit from said first and second binary signals;
slowing down the speed of rotation of the engine while it is still rotating in the detected direction, by delaying the sparking of the ignition circuit with respect to a top dead centre of the engine; and
effecting the reversal of the rotation by sparking in advance with respect to said top dead centre of the engine.
According to further feature of the invention, an electronic apparatus is provided for reversing the rotation of a two-stroke internal combustion engine having at least one two-stroke cylinder-piston unit, comprising:
an engine ignition circuit;
a voltage generator having a permanent magnet rotor and a stator provided with a winding for generating an alternate voltage for powering the ignition circuit;
means for supplying phase signals correlated to the direction and speed of rotation of the engine; and
a microprocessor control unit, for controlling the phases of the ignition circuit and for effecting a reversal of rotation of the engine,
the apparatus comprising:
a bistable sensor having first and second conductive states, said bistable sensor being cyclically activable during the rotation of the engine for the generation of a first binary signal correlated to said first and second conductive states;
a circuit for generating a second binary signal correlated to the polarities of the alternate voltage for the ignition circuit;
the microprocessor control unit comprising signal inlets fed with said first and second binary signals, said control unit being programmed for determining speed and direction of rotation of the engine, and for controlling the ignition of the engine, during forward and reverse rotation, and for slowing down and reversing the rotation of the engine, on the basis of information obtained from said first and second binary signals.
According to a particular embodiment of the invention, the bistable magnetic sensor is positioned close to a peripheral wall of the rotor of the voltage generator to be cyclically subjected to magnetic pulses for switching over its states, provided by flux circulation means on the peripheral surface of the rotor, to obtain a binary signal having positive and negative front sides appropriately out of phase with respective to the top dead centre of a piston of the engine.
The magnetic sensor preferably comprises a bistable Hall-effect probe, with a suitable magnetic circuit optimized for sensing the magnetic flux which flows from appropriate apertures in the peripheral wall of the rotor of the voltage generator; in order to maintain a high degree of precision at switching time of the sensor, and at the same time ensuring a satisfactory sensitivity, said apertures for the passage of the flux extend in the axial direction of the rotor.
The holes for the passage of the flux must be in such positions that the axes of at least two consecutive holes are always facing the axes of magnetic poles of the voltage generator, having opposite polarities, at an angular distance correlated to the position identified by the top dead centre of the piston or pistons of the engine.
More in particular, by referring to the angular position of the rotor corresponding to the dead centre of one piston of the engine, the two apertures which allow the activation of the sensor will be disposed symmetrically with respect to the position of the sensor itself, at an angular distance ranging approximately from 40xc2x0 to 60xc2x0, so that the changeovers in the conductive state of the magnetic sensor and of the binary signal occur in positions which are symmetrical with respect to the position identified by the top dead centre of the piston, representing sufficiently advanced events with respect to the dead centre in both directions of rotation, thereby allowing control of the ignition by actuating even high advance angles in both directions of rotation.
According to a further aspect of the invention, the magnetic sensor is connected to the microprocessor of the control unit by means of an interface comprising a voltage comparator capable of supplying said first binary signal in relation to the state assumed by the bistable magnetic probe; the same line which supplies the control unit with information on the state of the magnetic probe is also used for supplying power to the probe itself.
According to a further feature of the invention, the axes of the magnetic poles of the stator of the voltage generator are be positioned in such a way that the zero crossing of the alternate voltage supplied by the same generator, corresponds to the angular positions of the magnetic poles of the rotor identified by the top dead centre or centres of the engine.
According to the invention, after a reversing control has been operated by a driver of the vehicle or a user, the engine is slowed down by controlling the ignition with a suitable ignition delay with respect to the top dead centre, by an appropriate deceleration law programmed and controlled by the microprocessor, acting upon the extent of such delay; when the engine has reached a pre-established optimal speed of rotation, a spark is generated for a suitably and amply advanced ignition with respect to the top dead centre, aimed at reversing the movement of the drive shaft before the involved piston reaches its top dead centre, and then controlling the ignition with a usual optimal advance to allow the engine to continue to rotate in the opposite direction.
The apparatus is capable of sensing the outcome of a reversing attempt thanks to the processing, by the control unit, of the signals provided by the bistable magnetic sensor and by the voltage generator, and is consequently capable of controlling any subsequent attempts, and if necessary of abandoning the reversing process, resuming the normal control of the advance whenever certain conditions occur, such as for example the failure of a certain number of attempts.
Furthermore, according to the invention, the command for reversal of the engine by the user is transmitted to the control unit through an interface designed to control all the inputs and outputs interacting with the user, said interface being connected to the ignition control unit by means of a serial communication channel.